In recent years, the use of wireless communication devices has greatly increased. Specifically, the use of mobile cellular telephones has become common place such that many users, or subscribers, to cellular services use cellular telephones with regularity. One particular advantage of mobile cellular telephones is that when installed in an automobile or otherwise used away from the home or office, cellular telephones provide users with the freedom of travel without losing the ability to be constantly linked to a communications net work.
The coverage area of a cellular telecommunications network including mobile cellular telephones is divided into smaller coverage areas called “cells” that use transmitters and receivers. As is well known in the art, the limited coverage area of each cell typically allows the radio channels used in one cell to be reused in another cell. In a typical cellular telecommunications network, as a mobile cellular telephone within one cell moves near or across the boundary of the cell, control circuitry associated with the cell monitors the signal strength to determine if it would be advantageous to transfer the call to the adjacent cell. Indeed, in one known scheme, if the signal strength to that mobile telephone from signals originating in the adjacent cell is stronger than the signal strength for signals originating in the present cell, communications with the mobile telephone are “handed off” (transferred) to the adjacent cell. Handoff can also include a transfer from one traffic channel to another traffic channel on the same cell or an adjacent cell.
Typically, the cellular network uses signal strength and/or some other signal quality measurement reported by the mobile devices as well as signal strength and other signal quality measurements performed by base station receivers to evaluate whether to hand off the call. Conventionally, if the signal strength or quality falls below a predetermined threshold, the system automatically initiates a call handoff. Unfortunately, if the signal strength or quality is well below the threshold at the time of the handoff, the communication link may be severed during the handoff. This is so because for the handoff to be successful, a certain call quality ordinarily must be maintained.
Therefore, a need exists for a method and system for controlling a call in a cellular telecommunications network to effect call handoffs, while improving quality of service and/or minimizing dropped calls resulting from such handoffs.